The present invention relates to a feed roller assembly for feeding sheets of paper in an image forming apparatus for forming images on the sheets. The invention also relates to an image forming apparatus fitted with a feed roller assembly.
It is strongly demanded that an image forming apparatus for forming images on sheets of paper being fed in the apparatus should form images at a higher speed. In order to form images on sheets of paper at a higher speed, it is necessary to feed the sheets at a higher speed. In an image forming apparatus, a feed roller set feeds sheets of paper, as disclosed in JP-2002-160844A, for example.
The feed roller set consists of a driving roller assembly and a driven roller assembly. Each of the roller assemblies includes a shaft and rollers, which are fixed to the cylindrical surface of the shaft at intervals along the shaft. The driven roller assembly is biased toward the driving roller assembly so that the cylindrical surface of each of the rollers of the driving roller assembly can be in compressive contact with the cylindrical surface of one of the rollers of the driven roller assembly. A motor rotates the driving roller assembly with the driven roller assembly so as to feed the sheets through the roller nips between the assemblies. The rollers rotate at high speed to feed the sheets at high speed in the apparatus.
While the rollers are rotating at high speed, their cylindrical surfaces rub against the sheets, so that paper dust is produced from the sheets. The paper dust includes short cellulose fibers and part of the bulking filler and bleaching agent which were added when the sheets were produced. The compressive force between each of the rollers of the driving roller assembly and the associated roller of the driven roller assembly is greatest in the middle of the rollers, so that the paper dust produced from the sheets and sticking to the cylindrical surfaces of the rollers moves from the middle of each of the rollers to both ends of the roller and falls on the cylindrical surfaces of the shafts between the rollers. The fallen paper dust accumulates around the shafts between the rollers.
The accumulating paper dust is heated by its friction against the cylindrical surfaces of the shafts rotating at high speed, and/or against ends of the rollers rotating at high speed. As a result, the apparatus may break down or fire.
One object of the present invention is to provide a feed roller assembly which prevents the paper dust accumulating around its shaft between its rollers from coming into contact with the shaft and the ends of the rollers rotating at high speed with the shaft.
Another object of the present invention is to provide an image forming apparatus prevented reliably from breaking down or firing due to the frictional heat generated by its feed roller assembly.